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Abstract
Polyphenolic compound catechins ((-)-epigallocatechin gallate (EGCG), (-)-epicatechin
gallate (ECG) and (-)-epigallocatechin (EGC)) from green tea were evaluated for their
ability to inhibit influenza virus replication in cell culture and for potentially
direct virucidal effect. Among the test compounds, the EGCG and ECG were found to
be potent inhibitors of influenza virus replication in MDCK cell culture and this
effect was observed in all influenza virus subtypes tested, including A/H1N1, A/H3N2
and B virus. The 50% effective inhibition concentration (EC50) of EGCG, ECG, and EGC
for influenza A virus were 22-28, 22-40 and 309-318 microM, respectively. EGCG and
ECG exhibited hemagglutination inhibition activity, EGCG being more effective. However,
the sensitivity in hemagglutination inhibition was widely different among three different
subtypes of influenza viruses tested. Quantitative RT-PCR analysis revealed that,
at high concentration, EGCG and ECG also suppressed viral RNA synthesis in MDCK cells
whereas EGC failed to show similar effect. Similarly, EGCG and ECG inhibited the neuraminidase
activity more effectively than the EGC. The results show that the 3-galloyl group
of catechin skeleton plays an important role on the observed antiviral activity, whereas
the 5'-OH at the trihydroxy benzyl moiety at 2-position plays a minor role. The results,
along with the HA type-specific effect, suggest that the antiviral effect of catechins
on influenza virus is mediated not only by specific interaction with HA, but altering
the physical properties of viral membrane.